1. Field of the Invention
The present invention relates generally to control apparatus and method for an internal combustion engine with variably operated engine valves in which a variable valve drive unit through which an open-and-closure operation of one of the engine valves, viz., an intake valve is arbitrarily controllable is installed and which controls a closure timing of an intake valve to regulate an air quantity sucked into an engine cylinder.
2. Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 11-117777 published on Apr. 27, 1999 (which corresponds to a U.S. Pat. No. 6,039,026 issued on Mar. 21, 2000) exemplifies a previously proposed electromagnetically operated engine valve open-and-closure timing controlling apparatus for an internal combustion engine.
In the previously proposed electromagnetically operated engine valve open-and-closure timing controlling apparatus, open-and-closure operation of engine valves, for example, an intake valve can arbitrarily be controlled using variably operated engine valve drive mechanisms and an intake air quantity sucked into a corresponding engine cylinder is controlled by varying a valve closure timing of the intake valve, with the intake valve closure at a time point when a piston reaches to an intake stroke bottom dead center as a latest valve closure timing (so called, an earlier valve closure timing control).
Since such an electromagnetically operated valve open-and-closure timing controlling apparatus as described above has an object of an improvement in a fuel consumption through a non-throttle drive (viz., a state wherein an engine throttle valve of an electronic control type is at a full open state) (also-called, a reduction in a pumping loss), the engine is basically driven, an air pressure within an intake air passage being equivalent to the atmospheric pressure. An air quantity to be sucked within the cylinder is controlled by a cylinder volume at the time point of the closure of the intake valve.
In order to cope with an occurrence in a request to develop a vacuum pressure in the engine during a low engine coolant temperature, from a purge system of vaporized fuel, from a blow-by gas ventilation system, and/or from a brake master vac.(a brake booster of a master cylinder of a vehicular brake system), it is often necessary for the electromagnetically operated engine valve open-and-closure timing controlling apparatus to further control a position of the electronically controlled throttle valve to develop a desired vacuum pressure within a portion of the intake air passage located downstream to the throttle valve.
While the air quantity to be sucked into the engine cylinder is controlled according to the valve closure timing of the intake valve, the air quantity is controlled according to a cylinder volume at the time of closure of the intake valve. Hence, in a case where a pressure variation occurs within the intake air passage, an air density is accordingly varied so that an intake air mass within the corresponding engine cylinder is also varied. Especially, in a case where a target vacuum pressure is variably controlled in response to the occurrence in the request to develop the vacuum pressure, the previously proposed electromagnetically operated engine valve open-and-closure timing controlling apparatus described in the Background of the Invention cannot cope with such a pressure variation as described above in the intake air passage.
It is therefore an object of the present invention to provide control apparatus and method for an internal combustion engine which can achieve a cylinder intake air mass which meets with a demanding torque irrespective of a variation in air pressure within a portion of an intake air passage located downstream to an electronically controlled throttle valve even if a desired vacuum pressure is provided in an intake air passage while performing an air quantity control through a variably operated engine valve and which can improve a control accuracy of intake air quantity.
According to one aspect of the present invention, there is provided a control apparatus for an internal combustion engine, comprising: a variably operated intake valve enabled for its open-and-closure operation to be arbitrarily controlled; a target air quantity calculating section that calculates a target air quantity to be sucked into an engine cylinder on the basis of an engine driving condition; a target vacuum pressure calculating section that calculates a target vacuum pressure on the basis of the engine driving condition; a throttle valve controlling section that controls a throttle valve disposed in an intake air passage of the engine to achieve the target vacuum pressure; and an intake valve open-and-closure timing controlling section that calculates and controls valve open and closure timings of the variably operated intake valve to achieve the target air quantity, the valve closure timing of the intake valve being varied in accordance with a vacuum pressure developed within a portion of the intake air passage which is located downstream to the throttle valve.
According to another aspect of the present invention, there is provided a control method for an internal combustion engine, comprising: providing a variably operated intake valve enabled for its open-and-closure operation to be arbitrarily controlled; calculating a target air quantity to be sucked into an engine cylinder on the basis of an engine driving condition; calculating a target vacuum pressure on the basis of the engine driving condition; calculating an opening of a throttle valve disposed in an intake air passage of the engine to achieve the target vacuum pressure; controlling the opening of the throttle valve in accordance with a result of calculation of the opening of the throttle valve; calculating valve open and closure timings of the variably operated intake valve to achieve the target air quantity; and controlling the valve closure timing of the variably operated intake valve in accordance with a result of calculation of the valve closure timing of the intake valve, the controlled valve closure timing of the intake valve being varied in accordance with a vacuum pressure developed within a portion of the intake air passage which is located downstream to the throttle valve.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.